Modern web applications face a constant barrage of attacks targeting authenticated user sessions, including Cross-Site Scripting (XSS), Cross-Site Request Forgery (CSRF), clickjacking, Cross-Site Leaks (XS-Leaks), and even Spectre. Fortunately, recent advancements in web browser security provide developers with powerful tools to mitigate these threats. This talk delves into the latest web platform security features, equipping you with the knowledge to protect your applications. We'll explore CSP3, Trusted Types, Fetch Metadata headers, and COOP, demonstrating how these mechanisms can effectively thwart entire classes of web vulnerabilities.